1. Field of the Invention
The present invention relates to remedying a defect in a glass substrate which constitutes a display panel.
2. Description of the Related Art
There have been many cases that a glass substrate is used as a substrate for constituting a flat display panel such as a liquid crystal panel or a plasma display panel (PDP). Requirements for the glass substrate for a flat display (hereinafter simply referred to as a “glass substrate”) have been more and more difficult as enlargement of display has been accelerated in recent years.
One of the requirements for the glass substrate is a reduction in glass substrate defect. Here, the glass substrate defect indicates an internal defect such as an internal bubble or an internal foreign matter, and a surface defect such as a protrusion or a scratch formed on a surface of a glass substrate.
When a flat display is formed with the use of a glass substrate having a defect, it causes a display defect such as a bright dot or a black dot in the vicinity of the defect. On this account, it is preferable that a glass substrate include as little defects as possible.
Here, the following explanation deals with how such the glass substrate defect occurs.
In a process of melting a glass material in producing a glass substrate, air comes into the material or a gas is emitted from a fire-resisting material, thereby causing a bubble in the melted glass material. As such, an internal bubble is caused. Further, there are some glass materials to be used that generate a gas themselves. Such internal bubbles exist at a certain ratio depending on a volume, and it is not easy to decrease the ratio. In a case where a bubble existing inside a glass substrate is located close to a surface of the glass substrate, the glass substrate may include a protrusion (including a projection or an undulation) on the surface thereof.
Meanwhile, an internal foreign matter is caused due to (i) a raw material, or (ii) contamination from outside. As the internal foreign matter caused due to a raw material, there are (a) a case where a glass material is not melted and remains as a foreign matter, and (b) a case where a material that is not easily melted is mixed in a glass material. Further, as the contamination from outside, there is a case where a fire-resisting material that has been used for melting a glass material is mixed in the glass material and remains as a foreign matter. In a case where such a foreign matter existing inside the glass substrate is located close to a surface of the substrate, the glass substrate may include a protrusion (including a projection or an undulation) on the surface of the glass substrate, similarly to the internal bubble.
A protrusion formed on the surface of the glass substrate is, as has been already described, a surface defect that is caused due to an internal bubble or internal foreign matter.
Further, a scratch formed on the surface of the glass substrate is caused such that, in a processing step of carrying out an edge process with respect to glass substrates cut out from a large glass plate, which is called a primitive plate, the glass substrates come into contact with each other.
Here, though this is not the one for dealing with the glass substrate defects, there has been known a technique for eliminating a bright dot defect, in which technique a recess is formed on a region corresponding to a defective pixel in a glass substrate, and a light-shielding resin is filled into the recess, so that leakage of light is prevented (see Patent Documents 1 and 2).
Further, there has been also known a polishing apparatus for removing a very small protrusion by grinding the protrusion formed in a color filter of a liquid crystal display panel (see, for example, Patent Document 3).
Moreover, there has been a method for remedying a defect, such as a pin hole and a void, of a dielectric film provided on a full plate of a plasma display apparatus (see, for example, Patent Document 4).
However, as described above, any of the techniques disclosed in Patent Documents 1 through 4 are not techniques for dealing with the glass substrate defects.
[Patent Document 1]
Japanese Unexamined Patent Publication, Tokukaihei, No. 5-210074 (published on Aug. 20, 1993)
[Patent Document 2]
Japanese Unexamined Patent Publication, Tokukai, No. 2005-189360 (published on Jul. 14, 2005)
[Patent Document 3]
Japanese Unexamined Patent Publication, Tokukaihei, No. 6-313871 (published on Nov. 8, 1994)
[Patent Document 4]
Japanese Unexamined Patent Publication, Tokukai, No. 2000-294141 (published on Oct. 20, 2000)